1. Field of the Invention
The present invention relates to a display matrix incorporating an assembly of light-transmitting optical fibers and, more particularly, relates to such matrix having selectively operable control means to regulate light passage from the optical fibers to the display.
2. The Prior Art
Several types of technology are known to exist for making display panels with variable messages, intended primarily for road use.
Prisms have been used in such panels which enable two messages and a blank surface to be displayed. Panels have been constructed from matrices of dots which display messages in alphanumeric and graphic symbols. Matrices are versatile since the number of possible messages is practically unlimited.
Matrix type display panels may be of the active type, such as matrices of lamps, electroluminescent diodes, plasmas, etc., or the passive type, such as matrices with magnetically-operated elements. These types of systems have disadvantages. Matrices incorporating lamps are heavy and require substantial supports. Systems incorporating diodes and plasma are difficult to see in daylight and may be washed out by bright sun or artificial light. The passive systems do not always provide the desired visual impact and limits the display of colors.
Systems incorporating optical fibers, or light conductors, provide a very strong visual impact, even under adverse conditions, such as fog, rain, light glare, etc., and therefore have proven advantageous. Moreover, optical fibers enable messages to be displayed in any desired color. However, the number of possible messages are limited by the construction of such systems, and generally can not exceed six or seven different messages.
German Patent Application No. DE-A-2 831 174 discloses a display matrix of the above type in which the optical fibers associated with occulting devices interposed in the path of the light between a light source and the front of the matrix and is capable of modifying the color and/or intensity of the light emitted to the front of the matrix. Devices controlling the occulting devices make it possible selectively to control occultation of determined groups of fibers to change the display as desired.
Occulting devices of the prior art have included the optoelectronic type, such as liquid crystals, etc. As an example, U.S. Pat. No. 3,909,823, issued to Knowlton, discloses the use of a liquid organic crystal material as a light shutter. These devices, however, have not been satisfactory for applications to displays on roads and highways. On one hand, these devices have been highly susceptible to operational disturbances due to very low temperatures in winter and high temperatures when they are exposed to the sun. On the other hand, since optoelectronic devices never completely occult the light, the displayed messages are blurry and imperfectly defined.
The occulting devices of the prior art have also included electromechanical types, such as blocking screens moved in translation by jacks, or pivoting shutters or valves controlled by electromagnets, such as disclosed in U.S. Pat. Nos. 3,140,553, to Taylor and 4,040,193, to Matsuda et al. In the first case, the lateral dimensions are relatively large and, when used with optical fibers, do not permit the close downstream grouping of the fibers which is necessary for good luminosity of the display. In the second case, the slightest interruption of current causes all the valves to collapse, thus erasing the message. In both cases, the system is noisy and, moreover, permits only two positions: occultation or the absence of occultation. It does not permit variable messages in several colors to be made on the same matrix, which is necessary for representing certain road signs.
Another serious disadvantage of the prior-art electromechanical types of occulting devices is their relatively long response time, typically in excess of 1 ms. Due to the large number of matrix elements customarily used to form a display, the long time required by each occulting device to respond to a control signal to change its state of occultation results in an excessively long time to create or change a message.